1. Field of the Invention
This invention relates to an apparatus provided with an observation unit and using the operations of various functions and designed so as to be capable of selecting and setting functions by the direction of the operator's visual axis, and is particularly effective for a still camera or a video camera. Also, an apparatus for detecting the direction of visual axis according to the present invention is designed such that even if the position of the operator's eyes is wrong in the spacing and/or aligning from a predetermined position, it is compensated for and a result of detection of the direction of visual axis which is practically usable is obtained.
2. Related Background Art
Apparatuses for detecting the direction of the visual axis of an eye to be examined are known.
For example, the method described in Journal of Optical Society of America, Vol. 63, No. 8, pp. 921 and so on or the method disclosed in Japanese Laid-Open Patent Application No. 61-172552 projects light rays onto the front eye part of an eye to be examined and utilizes the Purkinje image which is the reflected image by the cornea or the crystalline lens.
A television camera which receives the reflected light by the cornea of the operator and detects eye movement and utilizes the result in auto focusing is disclosed in U.S. Pat. No. 4,574,314.
Apart from this, a construction as shown in FIG. 15 of the accompanying drawings has been proposed as an eye axis detecting method using the outline of iris. This method utilizes the fact that the iris is lower in reflectance than the sclera and detection of the boundary between the two is relatively easy, and both horizontal sides of the periphery of the iris (the boundary portion between the iris and the sclera) are first illuminated in the form of a spot or in the form of a strip by a light source LS. The reflected light therefrom is received by two light receiving elements PD, and the amount of movement of the eyeball in the horizontal direction (the angle of rotation) is detected from the differential signal thereof. Also, the amount of movement of the eyeball in the vertical direction is detected from the sum signal of the two light receiving elements PD. An infrared light emitting diode is used as the light source LS and infrared photodiodes are used as the light receiving elements PD, whereby a feeling of physical disorder to human eyes is eliminated.
However, this apparatus is based on the premise that it is used with the optic axis of the detection device being brought into coincidence with the optic axis of the eye to be examined and therefore, it is unsuitable for a case where as in an observing eye which is inadvertently looking into the eyepiece of an optical instrument such as a single-lens reflex camera, there is a great possibility that eccentricity is included between the optic axis of the eyepiece and the eyeball axis.
Incidentally, the necessity of detecting the direction of the visual axis of the eye to be examined which is looking into a single-lens reflex camera is based on the fact that the advance of the automatic focus detecting technique in cameras has led to the provision of distance measuring fields for detecting the focus not only at the center of the picture plane but also at a plurality of locations, which in turn has led to the necessity of providing input means for quickly selecting one of them, or the fact that there is a desire to simplify means for changing over the other conditions of the camera, for example, the average photometry and the priority photometry or selecting and inputting one of a plurality of photographing modes. Such necessity exists not only in cameras, but also in observation apparatuses such as microscopes or position detecting apparatuses or the like.
Where an observer looks into an eyepiece, there is more or less difference in the distance of distinct vision from person to person or there arises an individual difference in the spacing between the eyepiece and the observing eye due to habit or wearing of spectacles.
However, if the spacing between the detection apparatus and the observing eye is not constant when information is to be obtained about the observing eye, the reliability of the detected information will unavoidably be remarkably low, and this is inconvenient for a use which requires accurate measurement.
A related art is described in U.S. patent application Ser. No. 327,784 by the assignee of the present invention. Other related arts include U.S. Pat. Nos. 3,542,457, 3,699,248, 3,923,370, 4,019,813 and 4,034,401. On the other hand, the operation of selecting the photographing modes of still cameras recently used will hereinafter be briefly described with reference to FIG. 16 of the accompanying drawings. In the figure, the reference numeral 31 designates a dial for information selection, the reference numeral 32 denotes an exposure control mode selecting switch, the reference numeral 33 designates an exposure correction button, the reference numeral 34 denotes a film wind-up mode selecting button, and the reference numeral 35 designates a focus mode selecting button. With the depression of one of the buttons 32 to 35, the dial 31 may be rotated so as to select desired one of various modes.
In the case of such selecting operation, there has been the cumbersomeness that the photographer must look aside the viewfinder each time he changes the mode.